Method of adhering particles to a support surface



sept. 27, 1966 R. D. ELL 3,275,466 A METHOD OF ADHERING PARTICLES TO A SUPPORT SURFACE Filed May z, 1965 5 sheets-sheet 1 gc-Tu...)

lNV EN TOR.

Sept. 27, 1966 R. D. KELL 3,275,466

METHOD OF ADHERING PARTICLES TO A SUPPORT SURFACE Filed May 5, 1965 5 Sheets-Sheet 2 I N VEN TGR.

RW Kem Sept 27, 1965 R. D. KELI. 3,275,466

METHOD OF ADHERING PARTICLES TO A SUPPORT SURFACE Filed May s, 1965 Y IN VEN TOR.

United States Patent O M 3,275,466 METHOD F ADHERING PARTICLES T0 A SUPPORT SURFACE Ray D. Keil, Princeton, NJ., assignor to Radio Corporation of America, a corporation of Delaware Filed May 3, 1965, Ser. No. 457,241 22 Claims. (Cl. 117-335) This is a continuation-in-part of patent application Serial No. 108,535, led May 8, 1961, now abandoned. Both applications were tiled by the same inventor and were assigned to the same assignee.

This invention relates generally to a method of adhen ing particles to a support. The invention is particularly, although not exclusively, directed to a method of forming a very thin layer of colloidal particles, such as phosphor particles, upon a support surface.

In referring herein to colloidal-size particles, no limitation to a particular size range ofparticles is intended. Rather, the term colloidal is used herein in its broadest sense to mean a particle of such size that the surface properties are dominant over the mass properties; for example, where surface forces cause a particle to be suspended in a liquid which has a lower density than does the particle.

In some applications, extremely thin phosphor layers are desired. One type of cathode ray tube particularly demanding in this respect -uses a luminescent screen composed of superimposed layers of different phosphors, each layer of which emits light of a different color. In the operation of such a tube, selective penetration of electrons into the screen is obtained either by varying the velocity of a single electron -beam or by using a plurality of diiferent velocity beams t-o selectively excite the various phosphor layers to produce color images. Since color output is a function of screen penetration by the beam, the superimposed phosphor layers `should be thin in order that screen penetration from one phosphor layer to another, and hence color selection, can be effected with a practical switching signal voltage. In addition to being thin, the screen layers for such a tube should be of uniform thickness and -relatively nonporous in the sense that they should be substantially free of interstices, holes therethrough, or cavities therein. Where interstices, holes, or cavities do exist, or where the layer has a thin spot, some electrons of the beam may pass through :one layer and excite the next, when in fact, this should not occur. In some forms of this screen, the phosphor layers a-re separated by inert spacer layers which may have substantially identical characteristics to the phosphor layers except that they are nonluminescent. Such spacer layers provide better color seperation with less critical control requirements.

In addition to thin phosphor layers being useful in cathode ray tubes operating on the screen penetration principle to provide color images, thin phosphor layers are also useful in other tube applications. For example, tube applications which require high resolution displays, such as image tubes and certain oscillograph tubes, find such thin layers useful.

Evaporated phosphor layers have been proposed in an effort to provide nonporous, thin phosphor layers. However, evaporated phosphor layers are typically relatively low in light output efi'iciency. On the other hand the relatively highly eicient phosphor layers of sedimentarysize particles, such as are commonly made by settling the particles through a liquid cushion and onto a `support surface (substrate), are not suitable for such thin layers because of the relatively large size of the phosphor particles. The large size phosphor particles are themselves larger than the desired layer thickness. Moreover, such layers of sedimentary particles are inherently porous due to the 3,275,466 Patented Sept. 27, 1966 ICC large interstices between particles, which are loosely packed. V

In addition to the layers described above, thin uniform layers of particles of other electronically-active material are needed in a multitude of applications. For example, layers of magnetic, photoconductive, ferroelectric, electrically-insulating, electrically-conducting, and elect-ronemissive particles may be desired. As with phosphor particles, sedimentary-size particles may be too large, while vapor-deposited layers may be lacking in some important characteristic.

An object of this invention is to provide a novel method .of adhering particles to a support surface.

Another object is to provide a novel method of preparing thin, uniform layers of particles upon a support `surface.

A further object is to provide a novel method for preparing thin, light-transmitting luminescent screens comprising one or more layers of phosphor particles, which laye-rs are characterized by relatively uniform thickness or surface-to-surface ydimensions and nonp-orous texture, and which have relatively high light output eiciency.

Another object is to provide a new method of making luminescent screens which comprise one or more layers of tightly packed phosphor particles.

Generally, the novel method may be Iused to make a structure including the elements of: (a) a support surface and (b) particles. The support surface may be Van extended area of generally planar conguration or may be the surfaces of particles which are many times larger than the particles to be adhered to the support surface. The support surface may be the surface of a structural member or may be the surface of a layer adhered, either directly or indirectly to a structural member, as in a multiple layer embodiment. Any particles which are insoluble may be used in the novel method.

By the novel method, one only of the elements, either (a) the support surface or (b) the particles, but not both, is coated with a particle-adsorptive material; for example, gelatin. Then, the coated element is washed in a solvent for the coated material until substantially no coating materia-l can be washed from the coated element, thus leaving an adsorbed film of the material on the element. Then, the support surface is contacted with a dispersion of the particles in a quantity of liquid, the liquid of said dispersion being substantially free from particle-adsorptive rnaterial, whereby pa-rticles from the dispersion adhere to the support surface. The remaining dispersion is then washed away.

The process may be repated as many times as desired to build up the thickness of the particle layer, provided, in each cycle of the process, an adsorbed lm of material is present on one, but not both, -of the elements. In one form of the process, the support surface is coated With the particle adsorptive material, washed, and contacted with a dispersion of uncoated particles, and then this sequence of steps is repeated. In another form of the process, two dispersions are prepared; one a dispersion of particles that have been coated with the particle-adsorptive material and washed until no further material can be washed from the coated particles; and the other a dispersion of uncoated particles. The support surface is contacted with the one dispersion, is rinsed, is contacted with the other dispersion, is rinsed, and then this sequence of steps is repeated.

My invention may be used as a method of laying down a layer of phosphor particles to provide a novel luminescent screen by the use of particle-adsorbent nlms to which phosphor particles will be attracted and adhere. Such a film is interposed between a support surface and phosphor particles which are to be formed into a layer on the support surface. The support surface may be that of a faceplate or large base particles cle layer is to be formed. The method may, for example, be practiced either by forming such a lm on the support surface and then bathing it witha liquid dispersion containing the layer-forming phosphor particles, or else the may be formed on the layer-forming phosphor particles themselves and then the support surface bathed with a `liquid dispersion of the filmed phosphor particles. either case phosphor particles adhere to t-he support surface in a layer-like deposition. f

According to one embodiment of the method of my invention,` a support surface such asa glass faceplate is covered with such an adsorptive lm. The lm isthen covered, such as by bathing, with a liquid dispersion of phosphor particles. This results in `particles adhering to the, lm. The excess dispersion is then removed. Thesel steps maybe repeated Iany number of times to buildup a layer of phosphor particles to any desired thickness.

Using the method of my invention, a luminescent screen .may be prepared which comprises at least one layer built up of one or more depositions of closely packed phosphor particles. The particles are caused to adhere to each other` and/ or to a support surface by extremely thin films, such as gelatin films, interposed therebetween. The screen is substantially free of interstices whichl are of the same on which the phosphor partii order of size as, or larger than, the phosphor particlesV themselves, the layer being tightly packed and relatively nonporous.

Moreover, because phosphor particles are used, rather kthan an evaporated tilm good light output efliciency is obtained. Also, by using colloidal-sizepar.-

be made. y

The method of the invention may be used to Vprepare luminescent screens suitable for use in pentration type cathode ray tubes. Such screens may comprise a superimposed plurality of such phosphor particle layers in either: 1) extended layer form, or (2) multiple coated particle form. In extended layer screens each of the superimposed phosphor layers extends completely over the faceplate of the tube. In screens of multiple-coated ticles, very thin layers which are light-transmitting can particles the superimposed layers are formed as` super-.- imposed phosphor coatings on each of a multiplicity of relatively largey particles of, for example, glass or other `phosphor material, which particles 'are subsequently ,de-`

elect-rode` 26 by a terminal means sealed throughthe.

funnel 16 and schematically represented by the arrow 28.l A magnetic deection yoke 30, for example, is provided for deilecting ,the electron beam 20 to scan a raster over the faceplate 14.

a single colorlight output or white light output. Alternatively, the screen may comprisea plurality of superimposed layers of phosphor particles for producing light of f different colors.

The present invention may be used in making luminescent screens of a variety of types, including` screens for black and white cathode .ray tubes and also screens` for The invention may,.for example, be `used in making luminescent screens of the` multicolor cathode ray tubes.

type prescribed in 4the copending applicationSerial No. 108,565, of D. H. Pritchard entitled Electrical Devices and Methods filed May 8, 1961.

Where a plural layer screen 32 is provided and is born-` barded by electrons of different velocities, meansmay Abe`V ing to post acceleration;principles.y A separate lead-in Y means as indicated schematically by theiarrow 36 is vpro` vided for supplying suitable electric potentials -to the.`

plural layer screen 32 for effecting color selection. In

the case of a single phosphor layer screen 32,.the electrode' 34 may bepeither 'omitted or else included for the purpose of obtaining post acceleration oper-ation and its attendant advantages. 1

FIG.' 2 illustrate a luminescent screen 38` comprising-` a single layer 40 of phosphor particles `which could be usedin the tube 10.I The layer 40 is'characterized by having a thickness substantially greater than the size of the particles, thus resulting in a multiparticle thick layer'` n Because the particles are, in this kfree of perforations. example, of colloidal size, the layer v40 is very'thin Vand has good light transmissivity. Allight-reective `metal layer 41 of, for example, phosphor layer 40.'

FIG. 3 illustrates a three-'layer .luminescent screen `48 l which is suitable for use in the tube `10 for producingr Y color images. The luminescent screen 48 comprises multilayer screens, respectively, suitable for use ,in the tube of FIG. 1.

FIG. 4 is, an enlarged section of a modication of the multilayer screen of FIG. 3. FIG. 5 Voutlines a methodof making the screens of FIGS. l, 2, 3, and 4;

FIG. 6 is a section of a multiple-coated particle;

FIG. 7Vis a modication of the multiple-coated particle of FIG. 6;

FIG. 8 is a se'ction of a multilayer luminescent screen having FIG. 7 multiple-coated particles; and

FIG. 9 is a greatly magnified section of a phosphor layer.

In FIG. l, a cathode ray tube 10 comprises an envelope 11 including a neck 12, a faceplate 14, and an interconnecting funnel 16. An electron gun 18 in the neck 12 is adapted to project a beam 20 of electrons toward the faceplate 14. The neck 12 is closed at one end with a stem structurey 22 through whichk a plurality of` lead-ins 24 are sealed.- Suitable operating potentials are supplied to the electron gun 1'8 through the lead-ins 24v A conductive coating 26k is provided on the internal surface of the, funnel 16 and serves as an `accelerating electrode. A suitable high voltage potential is supplied to the coating As in the kscreen 48 of FIG. 3 inert separator layers 56` three superimposed layersk 50, 52, and 54 of colloidall The Ysuperimposed i phosphor layers Y 50, 52, and 54 may be in contact witheach other or alter phosphor particles.

nated, as shown, with inert (nonluminescent) separator layers 56 and58. Theseparator slayers 56 and 58 may comprise, for example, `particles of mica, vermiculite, colloidal silica, bentonite, kaolin, vanadium pentoxicle,l ory talc. 'These separator layers :may be put` down nzthe manner hereinafter described for putting down the phosphor layers 50, 52, land54`. The separator'layers 56 and 58 serve, among other things, to reduce color impurity of the light output. Thescreen 48 also includes a light- Y reflective metal backing layer `59 of,4 for example, aluv' minum. p

A modification ofY the screen 48 is shown in FIG. 4

`wherein like numbers yare used to identify like parts of the In FIG. 4 a luminescent screenr 60.

cle layers 50 and 52 superimposed on a relatively `thick,:

coarse particle, phosphor layer 62 comprised of largerthan-colloidal particles of, for example, sedimentarysize.

and 58 are .provided between adjacent phosphor layers,

phosphor layer 50.

aluminum, is deposited on thev i The screen 60 of FIG. 4 has, among other advantages, that of permitting a choice of screening techniques for the laying down of the fir-st phosphor layer 62. For example, the well-known settling method can be used.

Because, in the operation of the tube 10, it is not necessary that the electron beam penetrate through the phosphor layer adjacent the faceplate, that layer need not be extremely thin or nonp'orous. The porosity of the coarse particle layer 62 may be greater than that of the two layers 50 and 52 nearest the electron gun of the tube.

In a luminescent screen of colloidal phosphor particles, good light output can be obtained from thin, yet nonporous, phosphor layers. For example, good light output has been obtained from a 3-layer screen 48 having a total thickness of a few microns.

In laying down a phosphor particle layer, the novel method uses films of particle-adsorptive materials yhaving protective colloid properties. Some examples of protective colloid materials which have been successively used are gelatin, polyvinyl alcohol, and certain modified starches, such as :that sold by Hercules Powder Company and designated by the trade name Ceron-N. Many other :materials are known which have protective colloid properties and which may be useful in practicing this invention.

The protective colloid, as employed in this invention, when `applied to either (but not both) the phosphor particles or the substrate on Which the particles are to be deposited, results in obtaining the desired degree of affinity and ladhesion between the particles and the substrate.

CONTINUOUS EXTENDING LAYERS FIG. 5 outlines a method for making a thin phosphor screen such as is illustrated in either of FIGS. 2, 3, or 4.

In accordance with the outline of FIG. 5 the adsorbent film can be interposed between the particles and their support surface either by: (l) the filmed substrate method whereby a support surface is coated with Ian adsorbent film and then bathed with a dispersion of unfilmed particles, or (2) the filmed particle method whereby each particle is coated with an adsorbent film and an unfilmed support surface is then bathed with a dispersion of the filmed particles.

FILMED vSUBSTRATE METHOD To make a single phosphor layer `by the filmed substrate method such as the layer 40 of FIG. 2, an adsorbent film to which phosphor particles in a liquid dispersion will become attached is first provided on a support surface, such las the glass faceplate 14. Such a film may be provided by introducing a quantity of a solution of a suitable material having protective colloid properties in a solvent therefor, eg., a solution of gelatin in water, into .the envelope 11 to thus bring it into contact with the internal surface of the faceplate =14 so that the -faceplate is completely coated with a film of gelatin. The excess of the solution is then removed from the envelope by pouring it off.

The interior of the envelope is then Washed until substantially no particle-adsorptive material can be washed from the envelope. In preparing a gelatin film, several Washes of water insures that all gelatin has been removed except the film of gelatin that is adsorbed on the interior g-lass surface of the envelope.

I have found a solution of `approximately 0.1 percent gelatin in Water produces an excellent adsorbent film. I `have obtained satisfactory results with a concentration as low as 0.01 percent and as high as percent gelatin. When the concentration is made less than 0.01 percent, impractically large quantities of the gelatin solution are required. On the other hand, gelatin concentrations much greater than 10 pencent present a processing problem because of stability and viscosity of the gelatin solutions.

The aqueous gelatin solution is preferably adjusted to a pH 'of about 4 with the addition of an acid. Various acids can be used; glacial acetic acid has been found to be suitable. The degree of acidity, i.e., the pH, has not been found to be critical, except that too strong an acidification, e.g., a solution with Ia pH of much less than 3, may be detrimental to some phosphor materials. The acid appears to increase the affinity of the adsorbent gelatin film for the phosphor particles which are subsequently brought into contact therewith.

.Alternatively to, or in combination with, the adding of acid to the aqueous gelatin solution, an adsorbent film can be given an acid bath after it has been deposited on the support surface (faceplate 14). The acid bath may be performed by introducing a quantity of a suitable acid, for example acetic acid, into the envelope -1|1 and sloshing it over the adsorbent film on the surface of the faceplate y14. The excess acid is then poured olf.

Following the acid bath, or the acidfied gelatin application, as the case may be, a Water bath step is used. Water is introduced into the envelope l11 and thoroughly sloshed overthe filmed faceplate 14. The water is then poured off. The water bath step serves the purpose of removing surplus gelatin which is not in actual adherent contact with its support surface. Also, the water bath acts to remove excess acid left on the adsorbent gelatin film.

After pour-off of the Water bath, the faceplate 14 isV preferably spun to throw off all excess water. The adsorbent film can be dried to set the gelatin if desired. However, this is not necessary.

tFollowing the spinning off of the water, a dispersion of the desired phosphor particles in a suitable liquid, such as water, is introduced into the envelope 1'1 to bathe the gelatin filmed substrate. If desired, the phosphor dispersion'may be acidiiied as hereinafter described. A sucient quantity of the dispersion is used to insure good coverage of the [filmed surface of the faceplate 14. When the tfilrn of the gelatin solution is covered with such a phosphor-in-water dispersion, phosphor particles become attached tothe film in what is believed to be essentially a monoparticle thick deposition. |Inasmuch as settling is not the principal action Iwhereby the phosphor particles are deposited on the substrate, no harm resultsfrom agitation of the phosphor dispersion bath, and an agitated washing or bathing with the phosphor dispersion is the preferred procedure. The method of my invention is distinguished from settling techniques in that the washing with the phosphor dispersion, Whether agitatedV or not, is normally performed for a period of time, much less than would be required for a useful number of phosphor particles to settle out of the dispersion, even in the complete absence of any agitation.

Dispersion media other than water may be used, if desired. 'I prefer to use a phosphor-in-Water dispersion containing submicron size phosphor particles ina concentration of approximately 10 to 30 milligrams of phosphor for each cubic centimeter of water to produce the desired adsorption action.- Higher or lower phosphor concentrations than about 10-30 mg./ cc. can be used. Generally speaking, the more concentrated the phosphor dispersion the greater the rate of adsorption. Phosphor concentrations substantially less than 10 mg./cc. result in undesirably slow adsorption rates; phosphor dispersion concentrations substantially greater than 30 mg./cc. result in difficulties of centrifuging and redispersing the phospor particles. Phosphor particles up to three microns in size and larger have been deposited in layers by the method of this invention.

After the phosphor dispersion has thoroughly contacted the adsorbent gelatin lm, the excess dispersion is removed by pouring off. Following pour-olf of the phosphor dispersion, the phosphor layer adhering to the adsorbent gelatin may be given a Water wash to remove any `excess phosphor material which is not in adherent contact with the adsorbent film. l

` gelatin -flm `and a layer-like deposit of phosphor particles thereon. The layer of phosphor particles-is substantially of monoparticle thickness. AfterA a sufficient number of phosphor particles have vbeen adhered to the gelatin film to produce a certain particle concentration, further phosphor deposition'on the gelatin film substantially ceases. For some applications such a deposit of phosphor particles is sufficient. Howevenfor other applications denser or rthicker phosphor layers are preferred.

The particle density may be increased by adding to the above-described method a series of alternate acid and phosphor dispersion washes. Substantially complete coverage of the substrate can thus be obtained. IEach acid wash acts to renew the afnity of the gelatin film for additional phosphor particles so that further adsorption can take place.

Acid washes with acetic acid solutions having a pH of about 4 maybe used in making Vthe alternateacid Washes. I have further found that several, for example three or four, vof such additional acid Washes and phosphor dis,-

.persion washes appear to produce ymaximum density of the monoparticle thick phosphor deposit on theY gelatin film.` Additional alternate acid and phosphor dispersion 'washes deposit few, if any, phosphor particles onto theY gelatin film.

As an alternative to the above-described alternate acid and phosphor dispersion washes, particle `density may 'be strate-of a phosphor dispersion wash and before applical Ation `to the substrate ;of a subsequent additional gelatin .v solution `wash a dispersion of extremely fineparticlesA which are smaller than the phosphor particles being laid r increased `by acidifying the original phosphor dispersion,

i.e., giving it a pH less than 7, either before it is applied to the gelatin-filmed substrate or while the dispersion is still in contact with the filmed substrate. For example, 'I have found a pH of about 5 to [be suitable. Too great of an acidification of the dispersion, e.g., to a pH "of much less than 3, may detrimentally affect the phosphor material. By this simplified procedure, a sufficient number of phosphor particles can be adsorbed from a single phosphork dispersion application to produce a dense monoparticlethick phosphor` particle sublayer of substantially the same density quality as that produced using a series of alternate acid and phosphor dispersion washes.

Thicker phosphor layers may be obtained by following either one of two procedures. 'For example, thickness of the layer may be Ibuilt up by alternately repeating the gelax tin and phosphor dispersion lwashes. Teachings regarding water washes and proper pH adjustment of the gelatin solution according to the method steps set forth above are followed. Y n

Alternatively, the thickness of the phosphor particle layer may be built up in the form of superimposed sublayers of particles. By this alternative procedure, a dense monoparticle-thick sublayer is first laid down on a gelatin film by following either the alternate acid and phosphor dispersion wash steps or the simplified phosphor dispersion acidification procedure as described above. After one such sublayer has been laid down, it is given a water wash. A second gelatin film is then applied on top of the first sublayer and then a second dense phosphor particle sublayer is deposited onto the second gelatin film. This procedure may be repeated any. desired number of times to superimpose any desired number of dense phosphor particle sublayers.

In order to insure adherence of the phosphor particles to'each other and to their support surface after the resulting screen is finish-processed into a cathode ray tube, various alternative means can be employed. For example, the deposited phosphor layer.V or layerscan be'given`` a final wash with a silicatesolution, e.g., a 2 percent potas-` sium silicate solution. No subsequent water Wash is necessary, orin fact desired, lest the silicate `be removed. 1

Alternatively, they phosphor layers`can be -washed with a gelatin hardener ysuch as a small amount of 2 percent chrome alumor a 37 percent formaldehydesolution,`

after which the screen may be given a water wash. If desired, anadditional coating of just before the formaldehyde or chrome alum wash.

Another alternative prooedure for. improving adherence` is to apply to the substrate after application lto the subdown. The extremely fine particles are .preferablythough they need not necessarily be-luminescentand of the same phosphor as that of the phosphor layer being laid down. I have found that colloidal silica may be satis-l factorily used for the extremely fine particles. Such fine particles are adsorbed by the gelatin film between the `phosphor particles and act both to better secure the phosphor particles to the gelatin film and to improve packing; This procedure for improving Vadherence is particularly useful in combination with the above-described `simplified procedure of phosphor dispersion acidification for obtain-l ing dense monoparticle-thick sublayers. I have found that by acidifying a 30 mg./cc. .phosphor dispersion,;sub' stantially all of the phosphor particles Willbe removed therefrom and adsorbed on the gelatin film. 4Thus, a dispersion of the extremely fine particles, eg., colloidal silica, s

can be applied to the thus resulting phosphor sublayer by leavingiacontact .with the substrate the dispersion medium (Water) `of the phosphor dispersion fromwhich e the phosphor particles were removed and dispersing therein a quantity of colloidal silica-to of extremely fine particles. This procedure for improving adherence can be used in lieu of, or in combination with, the above-described alternative procedures` of Washihpg with potassium silicate, chrome alum, or formaldeyde. Y v Y A specific example of `making a screenof the continuous extending layer type bythe filmed substrate methodV will now be described.

Four grams of gelatin are added to 400 millilitersy of Y water. This isagitatedand then allowed to stand for thirty minutes. The gelatin-water solution is 'then warmed"l to 60 C. and maintained at this temperature for l5 minl utes. This insures that the gelatin will be completely dissolved. This 1 percent `gelatin solution is used either as is or is diluted as hereinafter specified.

A blue emitting phosphor layer of zinc sulfide activated with si1ver.(such asused in the commercial color kine-. scope 21CYP22) is laid down on the `faceplate as fol-v lows. Twenty grams of the :blue phosphor is given two washesin separate 250 milliliterquantities of water. With each wash, the phosphor'is agitated in the water, permittedl to settle for a few minutes, the water and line particles suspended therein decanted, andthe remaining settled phosphor recovered for subsequent use. The recovered phosphor, together with 0.06 gram ofl sodium pyrophosphate is dispersed in another 250 milliliters of water. The

sodium pyrophosphate serves `to prevent agglomeration yof the phosphor particles during a subsequent ball-milling thereof.

The phosphor dispersion vis then subjected to a ballmilling for 72 minutes, Ithen diluted with another 250 milliliters of water, and centrifuged at 1800 r.p.m. for 16V minutes. All particles below approximately 0.4 `of a micron in diameter together .with the excess of sodium pyrophosphate and water are discarded. Particles of approximately 0.4 to 5 -or 'l0 microns are recovered from the centrifuged material for subsequent use.: y

gelatin can be applied provide the dispersionA Some of the 1 -percent gelatin solution is adjusted by the addition of glacial acetic acid to bring the solution to a pH of approximately 4. A standard 21 inch rectangular faceplate panel is then coated with a film of this gelatin solution by covering it with the solution and gently tilting vand spinning it to slosh the solution thereover. The gelatin-coated faceplate is then washed with a flush of water. The gelatin coating step is then repeated to insure that the faceplate will receive a complete coverage with gelatin. This does not, however, act to provide a thicker gelatin co ating on the faceplate.

The gelatin-coated faceplate is then covered with water to a depth of about 2 inches. Five grams of the centri- -fuged blue phosphor powder are dispersed in 500 milliliters of water and sprinkled over the surface of the water in the faceplate. This is allowed to set for about l5 minutes, then most of the water is poured off. The remaining water and phosphor particles are then agitated by sloshing the dispersion over the faceplate by gently tilting and spinning the faceplate.

After a layer of the blue phosphor particles is adhered to the gelatin-filmed faceplate, the phosphor layer is washed with Water to remove all' loose particles therefrom and ythen coated with a F2 percent potassium silicate solution to improve adherence. 'I'he faceplate is then set on its edge and allowed to dry at room temperature.

The above-described gelatin, phosphor, and silicate coating steps are repeated once so as to produce a desired thickness layer of the blue phosphor particles on lthe faceplate.

A fi-rst separator layer of vermiculite is then laid down on the blue phosphor layer as follows. Two-hundred fifty milliliters of standard commercial expanded vermiculite, (such as that manufactured and sold by the Zonali-te Company of Trenton, New Jersey, and designated Terra- Lite) is added to 250 milliliters of water and mixed in a Waring household-type blender for 30 minutes. The

vermiculite-water mixture is then centrifuged for l minutes at 900 r.p`.m. This leaves in suspension vermiculite particles, the largest of which have a mass equivalent to that of about one micron spheres. However, the vermiculite particles are actuallyflakes with the greatest dimension of the largest ones probably-being about ten microns. This suspension is then concentrated by further centrifuging for one hour at 1800 r.p.m. to produce a concentration of about 18 milligrams per milliliter.

The faceplate is then again washed with the 1 percent gelatin solution having a pH of about 4 and then with water as before. The faceplate is then covered with the vermiculite suspension and spun at about 150 r.p.m. to provide a uniform depth of the vermiculite suspension over the surface thereof. After 15 minutes, the vermiculite suspension is removed and the faceplate is washed in water to remove all vermiculite particles not securely adhered to the gelatin film. Some particles of the ver- -miculite are, however, left adheringto the gelatin film on the blue phosphor layer. These steps of washing with gelatin solution, water, vermiculite dispersion, and water are repeated to provide 5' applications of vermiculite particles to produce a vermiculite layer having a total Weight of about 0.17 milligram per square centimeter.

A green emitting phosphor layer of zinc orthosilicate activated with manganese (such as used in the commercial color lkinescope 21CYP22) is then laid down on the first separator layer as follows. Twenty-five grams of the green phosphor are added to 250 milliliters of water and ball-milled for 74 hours. This is then allowed to settle for 48 hours and the top 5%: of the suspension removed for subsequent use. This produces a dispersion of green phosphor par-ticles which are not larger than about one half micron in size.

The faceplate is then Washed with a 0.1 percent gelatin solution and then given a water wash to remove all excess ofthe gelatin leaving a thin gelatin film thereon. The

faceplate is then dried to set ythe gelatin, and then given another water wash, and spun to remove the excess water.

The faceplate is covered with the green phosphor suspension and agitated by spinning in a manner as hereinbefore described in providing the vermiculite layer. The excess of the green phosphor suspension is removed from the faceplate and the faceplate washed with water to remove loose nonadhering green phosphor particles.

The steps of washing with :gelatin solution, water, green phosphor dispersion, and water are repeated to provide 6 applications of green phosphor particles to produce a layer having a total weight of about 0.29 milligram per square centimeter. This green phosphor layer is then washed with a 2 percent potassium silicate solution and dried.

A second vermiculite separator layer is then applied to the green phosphor layer in the same manner as the Ifirst separator was applied to the blue phosphor layer,- except ythat a 0.1 percent gelatin solution is used. Three applications of the gelatin and vermiculite particles are applied as before t-o produce a separator layer of about 0.14 milligram per square centimeter. After the last application of vermiculite particles is made, the surface is washedwith a 2 percent solution of potassium silicate.

A red emitting phosphor layer of ziuc-magnesium-cadmium-silicate phosphor activated with manganese is then laid down on the second separator layer as follows: a

13.65 gram quantity of this red phosphor is mixed with 273 milliliters of water and ball-milled for 70 hours. This phosphor water mixture is allowed to settle for 96 hours and the top 3A Irecovered for subsequent use. This produces a dispersion of red phosphor particles which are not larger than ab out yone-half micron in size.

Six applications of -gelatin and -red phosphor each are laid down on the -second vermiculite separator layer in a manner similar to that used in laying down the green phosphor layer. The six applications of the red phosphor particles produce a layer of about 0.35 milligram per `square centimeter. The red phosphor layer is then washed with a 2 percent solution of potassium silicate. The faceplate is then drained and dried at room temperature.

The faceplate having superimposed blue, green, and red phosphor layers is finally aluminized according to known techniques. A -film of nitrocellulose is spread `over the red phosphor `layer yby floating it on a pool of water To :make a single phosphor layer, such as the layer 40 of FIG. 2, by the filmed particle method there is first applied to each of the individual phosphor particles an adsorbent coating which will have an attraction to a support surface, such as the faceplate 14. The phosphor particles n to be so filmed may be bathed with a gelatin in water solution. The gelatin solution may be similar to -that described in the laying down of particle layers by the filmed substrate method. The phosphor particles are agitated in the gelation solution for a short period of time and then removed from the gelatin solution and thoroughly washed to remove all nonadhering gelatin therefrom. Each individual particle is coated with a thin film -of gelatin.

The gelatin-filmed phosphor particles may then be ideposited on a support surface such as the faceplate 14 by first dispersing the filmed phosphor particles in water and then bathing the faceplate 1-4 with the dispersion. Since the gelatin film ron the particles is adsorbent, the filmed particles will be attracted to and adsorbed by the support surface in a monoparticle thick layer thereon. The thorough washing -of the filmed particles referred to above is to prevent excess nonadhering .gelatin from contaminating the subsequent deposition dispersion. To allow such Vcontamination would result in both the particlesand the supportV surface being filmed with gelatin thus preventlng la proper adsorptive attraction.

According to one example, a filmed particle sublayer is provided as follows. A 1.0 percent solution of gelatin in water is adjusted to a pH of 4 by the addition of glacial acetic acid. The phosphor particles to be filmed are placed in a container togetherV with the gelatin solution and agitated for to 15 minutes.

The dispersion of` the phosphor particles in the gelatin solution is then per-I If.

dom from all unadhering gelatin by using test samples Y thereof to determine if the particles, when dispersed in clean water `can be adsorbed from the dispersion onto 1a clean support surface.

Each washing ofthe filmed particles is performed by dispersing the particles in an amount of water to provide a concentration of about 50 milligrams of filmed particles for each cubic centimeter of water. When a test of one of such dispersions results in `good adsorptive action, the dispersion is then used for the application of the phosphor particles to a support surface by the filmed-particle adsorptive adherence method.

The particle density and/or thicknessof the deposited layer may be increased by repeating the deposition cycle. Since the deposited particles in the filmed particle method have a particle-adsorptive film thereon, they will not attract, additionalY filmed particles. However, unlilmed particles will adhere to the filmed particles. Thus, a layer may be built up Ybycontacting the support surface with a dispersion of filmed particles, rinsing, then contacting the support surface With a dispersion of unfilmed particles, rinsing,. and` then repeating this sequence of steps.

MODIFICATION OF THE yMETHODS i Because a phosphorlayer may comprise sublayersA of phosphor particles, in order to obtain a relatively uniformly thick phosphor layer, it becomes desirable to provide relatively uniformly thick sublayers. the phosphor particles from which the sublayers are made range greatly in size, then a given sublayer may be relatively nonuniform in thickness. vided by a relatively large particle, of one sublayer chance to exactly overlie a correspondingly thick portion of the adjacent sublayer, then a thickened portion of the resulting phosphor layer results. Although, statistically, the occurrence of such a possibility is low, such possibility can be minimized by providing the phosphor particles within a relatively small range of sizes. With respect to nonuniform layer thicknesses, the size range is such as to include large particles or small colloidal particles because the range of particle sizes is more important than the abolute particles sizes. The range of `sizes of the phosphor particles is maintained Within minimum practical limits. I have found particle layers to be of quite uniform thickness where a substantial portion of `the smallest particles are not less than about one fourth lthe size of the largest particles. The practice of limiting the range of the particle sizes is applicable to either thefilmed substrate or filmed particle methods of the invention.

In accordance with a modification of the method, both phosphor layer thickness uniformity and nonporosity can be improved. Such modification involves a change only in the step of bathing the support surface with the phosphor dispersion.

Should a thick portion, as pro- The support surface isrstb'athed withia first dispersion containing lphosphor particles of given sizes. This bathing with phosphor dispersion is handled in the usual 1 It may involve Veither.` the filmed substrate yor filmed particle methods` of the way. as hereinbefore described.

invention. After bathing withithe first dispersion, "the support surface is bathed with'a second dispersion con-` taining smaller phosphor particles thanzsaid given sizes. Anacid wash maybe used to`promote adherence of phosphor particles from the second wash. Bathing withv the smaller particle dispersion serves to fill in the interstices Ybetween the previouslyk applied .larger particles, `thus reducing porosity and improving sublayer; thickness funi-Y formity. Because no adsorbent is applied to the support surface between the. baths with the first` and second dis-- persions, the smaller particles will adhere-only where a large particle :has not already adhered to the support surface. There kwill be substantially no` build-up of the smallerparticles on the larger particles.

In practicing this two-size particle modification of my` invention, the` earlier described preferred practice of using a small range of particle sizes in the phosphor dispersion can be advantageously used with respectsto both the first and second dispersions.,

MULTIPLE-COATED PARTICLE LAYERS The screens so far described have been of the extended layer type, which *compriseV a phosphor layer extending phor layers, and then depositing these coated base particles` onthe substrate in an extending continuous layer.

Such screens, .whereinY phosphor layers are superimposed j on indivldual particles, are, for some considerations, prel Such screens may be ferred forms of multilayer screens. referred to as multiple-coated particle screens. Y Y

Luminescent; screens for penetration-type lkincscopes.

as herein disclosed, whether of the extended layer typefor of the multiple-coated,particle`type, may` be considered as comprising a multiplicity offractional` areas of superl lmposed phosphor layers. In the case of multiple-coated particle screens, such a fractional area may comprise one or more of the multiple-coated particles.

FIG. 6 illustrates one form of luminescent material wherein glass particles .are `used 4as the bases for the several phosphor layers. The beads correspondto the support` surface` or substrate thatwas the basefor screens hereinbefore described. The beads used may, for example, be about 40 microns in diameter. For example, in FIG. 6a multiple-coated particle comprises a glass bead 70 which has Vformed thereon, in the order named: 'a layer of a first phosphor 71,-a first nonluminescent sepator layer 72, a layer of a second phosphor 73, a second nonluminescent separatorilayer 74, .and a layer of a third phosphor 75.1 T-he first, second and third phosphors eachV emit lightof a color different from the'others. Thus, an elemental multilayer screen is formed on'each bead. If

desired, a third nonluminescent layer 76 may be applied over-.the outer phosphor layer 75 to protect the particles during subsequent handling -and screen-making operations.

Instead of using a nonluminescent glass bead as the base Aand support surface forthe several phosphor layers, a phosphor particle itself canbe used `for this purpose.`

In such case, the base phosphor particle serves not only i as the base support surface but is suitably chosen to serve also as the first phosphorlayer, corresponding to the layer` 71 of FIG. 6. This is illustrated in FIG. 7.` i

FIG. 7 shows a multiple-coated phosphor particle which comprises a particle 80 of a first phosphor which has formed thereon, in the order named: a first nonluminescent separator layer 81, a layer 82 of'a second phosphor, a second nonluminescent separator layer 83, a layer 84 of a third phosphor, and a third nonluminescent layer 85 to serve as a protective coating. The particle 80 may, for example, be from to 40 microns in size. Each of the three phosphors luminesces in a different color.

FIG. 8 illustrates a multilayer luminescent screen made of the multiple-coated phosphor particles of FIG. 7. Because of the relatively small size of FIG. 8, the plurality of coatings on the multiple-coated particles thereof are represented schematically. The same general type of screen may be made from the multiple-phosphor-coated glass beads of FIG. 6.

The screen comprises a layer 91 of coated phosphor particles deposited on a substrate 92 such as a faceplate of a cathode ray tube. By way of example, the layer 91 is shown to have a thickness of substantially two particles. A screen thickness of two or more multiple-coated particles reduces the possiblity of nonluminescent area spots in the screen. Each multiple-coated particle .forms in effect a minute multilayer screen complete in itself which constitutes a minute fractional area of the entire screen.

An organic heat-decomposable film 93 is laid down over the coated particles. This may, for example, be of nitrocell-ulose or methyl methacrylate. An aluminum layer 94 is evaporated onto the film 93. The film 93 is then removed by volatilization and exhaust during tube 4bake-out and exhaust. The steps of providing the heatdecomposable film 93 .and the aluminum layer 94 may be similar to those used in the manufacture of other kinds of cathode ray tubes.

The multiple coatings of either the coated glass beads 69 or the coated phosphor particles may be applied using the general steps of the methods as hereinbefore described. That is, the coatings may comprise layers of particles applied by the surface adsorption principle using films of protective colloids to provide the adsorption. Moreover, adsorption applied layer coatings on base particles may be applied by either the filmed substrate (base particle) or filmed particle methods of the invention.

The phosphor and separator material particle dispersions should contain particles of a substantially smaller size than the glass beads 70 or base phosphor particles 80. Preferably, the dispersions contain phosphor and sepa- Arator particles of colloidal size, and base glass or base phosphor particles are of about 40 microns in size.

The steps of coating either the glass beads 70 or base phosphor particles 80 are essentially the same. The exception is that the glass beads70 are given a first phosphor coating which is not necessary when phosphor particles themselves are used as the base and support surface for the multiple coating layers. The steps of applying the coatings are substantially the same as those used to lay down extending continuous layers directly on .a faceplate except that the particle adsorption steps are carried out in a container 4other than the cathode ray tube bulb to be used for finished product.

In an example of making a multiple-coated particle screen, the following description is detailed with respect to the production of the coated phosphor particles of FIG. 9. Although this invention is not limited to any particular order arrangement of the different phosphor layers, for convenience of description, a structure of blueemitting phosphor base particle with green-emitting and red-emitting phosphor layers superimposed in that order will be described.

In such a structure, blue phosphor base particles are first put into a container and bathed with a particle adsorbing liquid, such as a gelatin in water solution. The mixture is agitated to washV the particles With the liquid; the particles are then allowed to settle; and the excess liquid is then poured off leaving a particle adsorbent film Yon the blue phosphor particles.

The adsorbent film is acidified according to teachings hereinbefore set forth. The film-coated base particles are then bathed or washed in Water. The water wash may be repeated several times.

Next, the first separator layer is laid down on the blue phosphor base particles by a similar bathing or Wash procedure. A suitable nonluminescent material such as silica or mica colloids dispersed in water is put into the container along with the filmed blue phosphor base particles. The materials in the container are agitated to coat the individual phosphor base particles With colloidal separator particles. The blue phosphor base particles are then allowed to settle and the excess separator dispersion is poured off. The blue phosphor base particles are then washed in water. Additional applications of separator particles, as desired, may be laid down to increase the separator layer thickness. This is done by again bathing the blue phosphor particles successively in the particle adsorbent liquid, Water, the separator dispersion Iand water. As hereinbefore detailed, either a plurality of alternate acid and phosphor dispersion washes or the simplified phosphor dispersion acidification procedure may be used to produce dense sublayers of the phosphor deposits.

When the first separator layer is thick enough, the green phosphor coating layer is applied on the first separator layer of the blue phosphor base particles. This is done in a manner similar to that by which the first separator layer was applied. The blue phosphor base particles rare subjected to a series of agitated washings in baths of the particle adsorbent liquid, Water, a dispersion of colloidal size green phosphor particles, and Water. Sufiicient number of applications of green phosphor particles are thus applied (if desired, procedures hereinbefore detailed to obtain dense sublayers may -be used) to build up the green phosphor layer to a desired thickness.

The second separator layer is then laid down over the green phosphor layer in a way similar to that in which the first separator layer was laid clown.

Next the red phosphor layer is formed on each individual coated particle. The red phosphor layer is laid down over the second separator layer in a way similar to that in which the green phosphor layer was laid down over the first separator layer. After the fin-al application of red phosphor'particles, the coated blue phosphor base particles lare washed in water to remove any remaining loose red phosphor colloids. This final wash step may be repeated a number of times, if desired.

After the final application of red phosphor material has been made, the coated particles may be given a final treatment to insure .adherence of the phosphor particle layers. This may be done -by Washing the coated Vparticles with a solution of formaldehyde, chrome alum, or potassium silicate as hereinbefore detailed. Alternatively, a final coating of the nonluminescent separator material may be applied over the red phosphor layer. Either the hardened gelatin or nonluminescent separator material coating serves to avoid any Washing away of the red phosphor layer in the subsequent process of putting the coated particles on a faceplate. Steps used to improve phosphor particle adherence as hereinbefore described may option-ally be performed at various times throughout the process of applying the particle coatings to the base particles.

After the final coating has been provided, the multiplecoated particles are deposited on the faceplate of a cathode ray tube in any one of a number of ways. For example, they may be applied by either slurry or settling techniques. Then, the layer of multiple-coated particles may be filmed and aluminized as shown in FIG. 8.

The coated particles may be stored either wet or dry until it is desired to put them on a faceplate. If stored wet, they simply remain in some of the final Wash water. If stored dry, the Water is decanted and they are simply dried at, for example, room temperature.

'for about 5 minutes.

-15` One specific example will now be describedfor preparing multiple-coated phosphor particles:

. Blue-emitting zinc sulfide phosphor activated with silver (commercially designated .as Z-20) is used for the ,base particles on which `subsequent phosphor coatings are to be applied. This phosphor material has a size distributionof about to 2O microns. Fifty grams of this material .are washed in water and allowedto settle. The wash Water together with any extraneous rrraterialsuspended` therein is discarded to leave only the desired 5-20 micron particle size material.

These 50 grams ofthe blue phosphor particles are. then placed in abottle together with a quantity of 0.1 percent gelatin-in-water solution having .a pH 'of 4. This is agitated for to 15 minutes and then allowed to settlek off leaving thewet 'blue phosphor particles with a gelatin film thereon. The .gelatin-filmed particles are then given three separate water washes in the bottle to rid them of nonadherent gelatin material.

A first silica separator layer coating is then applied to the `base blue phosphor particles as follows:

A dispersion of colloidal silica in water which has been adjusted to a pH of 4 with glacial lacetic acid is poured into the bottle containing the filmed particles. The silica in water dispersion-is ofv a concentration of 33 milligrams of silica for each milliliter of water. container is agitated for 10 to 15 iminutes and the` blue phosphor-base particles then allowed to settle for about 5 minutes. The silica-in-water dispersion is poured off and the blue particles washed `three times to remove all nonadherent silica therefrom. A Vdeposit of colloidal silica particles is left adhering to the gelatin-filmed blue phosphor particles. The successive washing ofthe blue phosphor particles in baths of gelatin solution, water, silica dispersion, and then water is repeated six timesy to Vbuild up a layer-of colloidal silica particles of about 0.2

milligram per square centimeter.

The silica-coated blue particles lare then coated with a layer of green-emitting manganese activated zinc orthosilicate phosphor -as follows:

A suspension of the green phosphor -as described in the making -of extended layer screens -is first centrifuged `to leave in suspension particles up to 0.8 micron in size.

This remaining suspension is: selected and then further centrifuged to provide a concentration of about 2O milligrams of phosphor per milliliter of Water. Six applica. tions of green phosphor particles are then'laid down on the silica coated blue particles `by repeating a series of gelatin solution water, green phosphor dispersion, and washes in a manner generally similar to the steps used in laying ydown the first silica separator layer. A layer of green phosphor particles having a total weight of about 0.3 milligram per square `centimeter is thus provided.

A second separator coating Yof colloidal silica is then deposited on the green phosphor layer. The procedure is generally the same as Was used to deposit the first silica separator layer on the blue base particles, with the excep- The The gelatin solution is then poured tion that the si'lica-in-w-ater suspension is adjusted to a pH of 5.5 and 8v applications are applied to produce a co1- loidal silica layer of about 0.2 milligram per. centimeter.

A red phosphor layer is then laid down on the second silica separator layer using a suspension of zinc-magnesium-cadmium silicate phosphoractivated with manga? nese as described with reference to the making of continuous extending layer screens. The base particles are successively washed by successivelyintroducing into the bottle, agitating and removing, washes of a 0.1 percentY gelatin solution having a Ph of 4, water, the red phosphor suspension, and Water. Six applicat-ions of the red phosphor are made to produce a layer of |about.0.4 milligram per square centimeter. Y

As -a final coating, the base blue phosphor particles are washed in a gelatin solution and then in a colloidal `silica dispersion to provide a thin layer of silica thereon.

'f other.

Multiple-coated particle screens offer a number'of advantages. For, example, the process of preparing the rnuldown of one does not necessarily affect the other. Moreover, these separate processescan be carried'out simultaneously thuslessening the complete fabrication time of` a finished tube. Moreover, if desired, existing facilities used in the manufacture of black and white cathode ray tubes may be used for laying down the coated` particles.

Anotherl advantage of multiple-coated particle screens is the ease with which they canV beV made to provide color emission uniformity during operation of the tube. Multiple-coated particles can be easily made with good phosphor layer` thickness uniformityfrom coated particle to coated particle. This'thickness uniformity isin turn providedV over the entire area-of a screen which is made of the multiple-coated particles. Y

PHOSPHOR LAYERS vIn phosphor layers prepared by the method of FIG. 5, the articles are essentially in contacting relation with each between particles. The adsorbent` films are :extremely thin, even compared to colloidal phosphor particles, and

constitute negligible percentages of the total mass of` the phosphor layer.

Laboratory examination of both a sublayer` of colloidall phosphor particlesand an adsorbent gelatin film has 'in di-v cated that the filmV thickness is a very small fraction by v Weight of the phosphor sublayer. The `adsorbent films` particle sublayers of the same phosphor material which have been laid down by the filmed substrate method using alternate acid and phosphor dispersion washes.

In laying down the layer of FIG. 9, an adsorbent gelatin film A is first provided on the substrate 14, shown specifically in FIG. 9 as a faceplate. A` subsequent bathing of the adsorbent film A with a dispersion'of phosphor parti-A cles will result in the phosphor particles a1 adhering thereto. A subsequent acid wash and then 1a second washing with the phosphor dispersion as hereinbefore described willi result in the` phosphork particles a2 adhering to the gelatin film A. Likewise, phosphor particles a3 will be deposited on the gelatinfilm A by a third phosphor dispersion wash after a second acid wash. Such alternate acid and `phosphor dispersion washes are repeated until substantially no additional phosphor-deposit occurs. The result is a rela'- tively dense monoparticle thick sublayer of phosphor par-` ticle4 al-ag-as, etc., which provides a substantially com-v plete coverage of the adsorbent gelatin film A. In similar'` manner, the adsorbent gelatin `film B is deposited on this first sublayer, of phosphor particles al-az-ag and a second monoparticle thick sublayer of phosphor particles bl-bzb3 is adhered tothe adsorbent film B.` These steps are again repeated to provide the adsorbent gelatin film C and the third sublayerr of phosphor particles ereg-c3, 1f

a thicker phosphor layer is desired, additional dense sublayers may be superimposed on the sublayery c1-c2-c3.

The uniformity of thickness and degree of packing of the particles of a layer of a given thickness can be stated Y 1n terms of the electron velocity volt-age at Whichboni-` barding electrons begin torpass completely through the layer. This velocity may be defined as the threshold penetratlon kvelocity voltage.

Thus, because the phosphor layer processing No substantial amount of binder material'exists Generally speaking, the electron penetrability of a given layer is dependent upon the layers average mass thickness (the product of the average mass-density and the average thickness of a relative large `area portion of the layer). Mass-density (hereinafter referred to simply as density) of a layer is determined by the kind of the material of the layer and by its packing (the ratio of volume of material to volume of space). A layer which has no spaces between particles thereof may be termed a perfectly packed layer. Such a layer might be formed, yfor example, by solidiiication of a molten mass of the material in question. Perfectly packed layers which are further characterized by substantially perfect thickness uniformity may be defined as layers of substantially perfectly uniform mass thickness. The ordinary evaporated, light-reflective aluminum layer, commonly used in cathode ray tubes, and gold or aluminum foils are examples of layers which have a substantially perfectly uniform mass thickness.

When the average `characteristics of relatively large areas of two layers are considered, a nonuniformly thick, loosely packed layer will impede the penetration of electrons to the same degree or absorb the same amount of energy from penetrating electrons, as a uniformly thick tightly packed layer, if the two layers have the same average mass thickness. However, this does not hold true when elemental areas of the layer are considered. As used herein, an elemental area is an area portion of a layer that has throughout its own area a perfectly uniform mass thickness. In particle layers, an elemental area is of the order of particle dimension or less in size. In perfectly packed layers, such as gold foil, elemental areas approach molecular dimensions in size.

Loosely packed layers are nonunifo-rm in density, having some elemental areas where the density of the layer is greater than the average density of the layer and sorne elementaal areas where the density is less than the average density of the layer. Similarly, nonuniformly thick layers have some elemental areas of greater than the average thickness and some elemental areas of less than the laverage thickness. Both these types of nonuniformity, where they exist, contribute to nonuniformity of the mass thickness of a layer. That is, the layer has some elemental areas where the mass thickness is greater than the average mass thickness of the layer and some elemental areas where the mass thickness is less than the average mass thickness of the layer. When an electron strikes a layer at one of the elemental areas of lesser mass thickness, it may pass completely through the layer even though an electron of the same velocity might not pass through a layer of the same average, but uniform, mass thickness.

Increasing the thickness of a particle layer increases both the absolute value of its threshold penetration voltage and also the ratio of its threshold Ipenetration voltage to that of a layer of the same average but perfectly uniform mass thickness. 'I'his is because the nonuniformity of the layer due to less than perfect packing is, by making the layer thicker, evened out by a statistical distribution of the spaces between phosphor particles. However, in order to give satisfactory service in a plural layer luminescent screen of penetration-type cathode ray tubes, the individual phosphor layers should be relatively thin in order to permit color selection at the least possible voltage differences and at the same time be sufficiently uniform in mass thickness so as to minimize color impurity. It has been found that such phosphor layers preferably should be thin enough that they have a threshold penetration voltage no greater than about 10 kilovolts and yet be of suiciently uniform mass thickness that their threshold penetration voltage is at least half that of a layer of the same average but perfectly uniform mass thickness. Phosphor particle layers may be laid down according to my invention which exhibit threshold penetration voltages which are only about 5 kilovolts, for example, and yet which are from about two-thirds to three-fourths that of a layer of perfectly uniform mass thickness. Comparing phosphor layers having equal average mass thicknesses of a given value: Whereas a layer of perfectly uniform mass thickness may have a threshold penetration voltage of about 8.8 kjlovolts; a layer according to my invention may have -a threshold penetration voltage of about 6 kilovolts; and a prior art settled layer m-ay have a threshold penetration voltage of only slightly greater than zero kilovolts.

There have been made and successfully operated multicolor luminecent screens of both the extended layer type and the multicoated-.particle type and monochrome screens of the extended layer type. Both the filmed particle method and the filmed substrate method have been used in making such screens. In e-ach case screens were obtained which: exhibited satisfactory adherence; have been ysatisfactorily used in cathode ray tubes; have been successfully subjected to 4standard tube processing procedures such as bake-out, envelope sealing, and aging; and have given good operational results and satisfactory light output.

LAYERS OF OTHER MATERIALS The novel method may be used to produce uniform thin layers of materials for other applications than for television. For example, in integrated circuits, micro-circuits, and some forms of transistors, thin insulating layers are required. These layers are sometimes produced by evaporation and deposition of the material in a vacuum. The novel method may be used to replace the vacuum evaportion process. The colloidal-size particles of the materials to be deposited are prepared, and the novel method may be used to produce thin layers of these particles. For example, insulating layers can be prepared by using, in the novel method, colloidal silica (SiOg), such as a silica commercially known as Ludox, marketed by E. I. du Pont de Nemours & Company, Wilmington, Del. The average particle size of this commercial material is about 100 A. A second insulating material that may be used in the novel process is an expanded Imica known as vermiculite, which may be prepared as plate-like colloidal-size particles. In fact, colloidal-size particles of any of the materials used in the separator layers 56 and 58 described above may be used as insulating layers for other applications.

Conducting layers may likewise be made using the novel method. For example, colloidal-size particles of gold (average particle size about -200 A.) may be used. In preparing conducting layers, the adsorptive films may be removed subsequent to deposit on the layer by heating the structure to volatilize the film, or by Washing the structure to dissolve the film material with a suitable solvent for it. For example, the deposited layer or layers may be washed with an aqueous solution of sodium hypochlorite to remove a substantial proportion of -adsorbed gelatin film. The structures deposited according to the novel method are stable after removal of the adsorbent films. This is beleived to be due to the inter-molecul-ar forces present in such structures. Colloidal-size particles of other metals may be used, such as zinc, platinum, or silver. With metals that have oxidized, the deposited layer may be heated in a reducing atmosphere to convert the layer to a true metal.

The novel method may be used to make thin magnetic layers. Such magnetic layers may be useful in magnetic memories in the field of computers. In the past, rnechanical limitations have limited the thickness of the layers of magnetic material which can be produced economically to approximately one mil. Layers of magnetic material of almost any desired thinness less than one mil may be conveniently made using the Vnovel method. For example, 0.1 mil thick magnetic layers of ferrite particles may be made. As an example, colloidal-size particles of a square loop ferrite such as a magnesium-manganese-zinc ferrite (described in U.S. Patent No. 3,031,406 to J. I. Sacco, Jr.) are deposited as -a layer on Ia refractory support using the novel method. Subsequently, the layer is heated at elevated temperatures to remove the adsorptive film material and to consolidate the layer. The layer may Patent No. 3,144,411 to F. Kulczar et al.) arel deposited as -a layer on a refractory support using the novel method. Subsequently, the layer is heated at elevated temperatures to remove the adsorptive film material yand to consolidate the layer. The layer may be metallized to provide electrodes and terminations thereto.'

In the field of photoconductors, thin layers of cadmium sulfide and cadmiu-m selenide may be deposited on various base materials using the novel method.

The 'adherence of colloidal-size particles to the adsorptive film is independent of the position of the adsorbent film surface, as illustrated by the individual coarse particles coated with layers of phosphor particlesand inert maferial (spacer) previously described. Because of this, it`

is possible to use the novel method to coat surfaces that are inaccessible with other methods.

TheA novel method may also be used to remove undesired colloidal-size particles from solutions in much the same way that certain resins are used for the removal of ions from solution. For example, in aqueous clay particle suspensions, colloidal-size clay particles, which are too small `for filtering, may be removed Vusing the novel method.l As an example, noncolloidal particles (for example sand) may be coated with adsorptive film and Washed until all soluble film material is removed, leaving a thin adsorbent` film on each grain of sand. The water containing the colloidal clay particles is then passed through thensand. The clay particles are adsorbed by the adsorptive film on the -sand `grains leaving clean water.

The invention has been described in terms of specific examples and embodiments. However, various changes and modifications may be made therein without departing from the spirit and scope of theY invention as defined by the following claims.

Unless otherwise indicated in the claims, the method steps recited therein need not be carried out in the order named.

What is claimed is:

1.V The method of making a Ystructure comprising the elements of: (a) a support'surface and (b) colloidal solid particles, said methods comprising the steps of:

(l) coating one only of said elements with a .protective colloid particle-adsorptive material, whereby at least a portion of said material ,isadsorbed to said one of said elements,

(2) then washing said one of said elements in a solvent for said material to remove unadsorbed material from said one of said elements,

(3) then dispersing said solid particles in a quantity of a liquid which is devoid of said material and in which said particles are insoluble,

(4) and bathing said support surface with said dispersion to adsorptively adhere said particles to said support surface. l

2. The method of claim 1 wherein, a step 1, said support `is coated with said particle-adsorptive material. Y

3. The method of claim 1 wherein, in step 1, said solid particles are coated with said particle-adsorptive material. 4. The method of making a luminescent Vscreen comprising lthe elements of: (a) a support surface and (b) phosphor particles, said method comprising the steps of: coating one only of said elements with a protective colloid particleadsorptive film, then washing said one of said elements in a solvent for said protective colloid, then dispersing -said phosphor particles in a quantity of 4said solvent which is devoid of said `protective colloid,

and agitatedly bathing said support surface with said dispersion to adsorptively adhere said phosphor particles to said support surface.

5. The method according to claim` 4 and whereink said support surface is the surface of a base phosphor particle which is of a size greater than and luminesces in a color different than do the phosphor particles in said dispersion.y

6. Themethod of making a luminescent screen com,-

prising alayer of phosphor particles on a support surface,

said method including the steps of:

coating each of said phosphor particles with'an adsorptive film to which said support surface Will adsorptively adhere,

washing said phosphor particles to remove the excesslof the material of said adsorptive film therefrom,

and agitatedly bathing said support surface lwith an aqueous dispersion of said filmed particles; While maintaining said support surface free of adsorptive film material other than that adsorptively coated on said particles to adsorbently adhere said filmed particles to said support surface.`

7.` The method of making a luminescent screen comprising/the steps of:

coating a support surface with a particle adsorptive film,

then removing that portion of the film materialwhich is not adsorptively adhering to said support surface by washing with a solvent for said material,

andthen contacting said film with an aqucuous dispersion containing phosphor particles which are sub-A stantially free of adsorptive film lmaterial to adsorptively adhere said particles to said filmed surface.

S..The method of making a luminescent screen comprising the steps of:

covering a support surface with a solution of particleadsorbent film forming material,

removingy the excess of said solution, Y

then washing said support surface with a solvent for said .material to leave an adsorbent film on said'` phosphor particlesonto said filmed support surface. 9. The method of making a luminescentscreen com prising the steps of:

bathing a support surface with an aqueous solution of a material selected from the group consisting of gelatin Vand polyvinyl alcohol,

then washing said support surface with water to remove any of said material which is non-adherent to said support surface,

then coveringY said surface with an aqueous dispersion containing phosphor particles which are substantially free of said material,

and then removing the excess of said dispersion after a period of time less than that which would be required for the deposition vof a .useful number of said phosphor particles Yonto said surface from asimilar dispersionrby a settling process.

10. A method of making a luminescent screen comprising a layer of phosphor particles on a supportsurface,`

ing a support member having a layer of phosphor particles thereon, said method comprising the steps of:

covering the surface of said support member with an acidified film of a protective colloid, washing said filmed surface with water, agitatedly washing said filmed surface with an aqueous dispersion which is free of said protective colloid and which contains phosphor particles which are to be deposited on said filmed surface,

washing said filmed surface with water,

and repeating the above-named steps to build up a layer of phosphor particles to a desired thickness.

12. The method of making a 'luminescent screen including a support member having a layer of phosphor particles thereon, said method comprising the steps of:

covering a surface of said support member with a particle-adsorbent film,

washing said surface to remove essentially that portion of the material of said film which is not adherently adsorbed onto said surface,

covering said film surface with a dispersion which contains phosphor particles and which is substantially devoid of particle adsorbent film material, the smallest of the phosphor particles contained in said dispersion not being less than one fourth the size of the largest,

and removing the excess of said dispersion to leave a layer of particles adsorbed on said film.

13. The method of making a structure comprising a support member having a layer of particles thereon, said method comprising the steps of:

bathing a surface of said support member with an aqueous solution of particle adsorbent film-forming material to deposit an adsorbent film on said surface, then Washing said surface with water,

then bathing said film with an aqueous dispersion of particleswhich is substantially free of any adsorbent film-forming material to deposit a dense sublayer of particles on said film,

and repeating the above-named steps to build up the thickness of said layer.

14. Ihe method of making a luminescent screen including a support member having a layer of phosphor particles thereon, said method comprising the steps of:

bathing the surface of said support member -with a solution of particle adsorbent material to provide an adsorbent film of said material on said surface, then washing said surface to remove therefrom the non-adherent portion of the deposited film material, then bathing said filmed surface with an adsorbent material free dispersion of phosphor particles of given sizes, and then bathing said filmed surface with a dispersion of particles which are free of adsorbent material and which are smaller than said given sizes.

15. The method according to claim 14 and wherein said particles which are smaller than said given sizes are phosphor particles.

16. The method of making a luminescent screen comprising a substrate having thereon a layer of base particles, each of which is coated all over with a layer of phosphor particles, said method including the steps of:

coating one of the elements selected from the group consisting of said base particles and said phosphor particles with 4an adsorptive film to which the other of said elements will adhere,

then washing said one of said elements in a solvent for the material of said adsorptive film,

dispersing said phosphor particles in a quantity of said solvent which is free of adsorptive film material, bathing the base particles with said dispersion to coat said base particles with said phosphor particles, and then depositing the phosphor coated base particles in a layer on said substrate. 17. The method of making a luminescent screen comprising the steps of washing a quantity of base particles with a solution Iof particle adsorptive material,

then Washing said base particles to remove the unadsorbed portion of said material therefrom, then bathing said filmed base particles with an acidified dispersion consisting essentially of solvent like that of said solution and phosphor particles to coat each of said base particles with a layer of said phosphor particles, and depositing said coated base particles in a layer on said substrate. 18. The method of making a luminescent screen comprising the steps of:

coating la multiplicity of base particles of a first phosphor which luminesces in a first color with films of a material selected from the group consisting of gelatin and polyvinyl alcohol, then washing said filmed base particles in water, then washing said filmed base particles with an aqueous dispersion of particles of a second phosphor which luminesces in a second color to provide a layer of said second phosphor particles on said base particles, said dispersion being substantially devoid of said material, said second phosphor particles being of sizes substantially smaller than the sizes of said base particles, and then depositing said coating base particles in a layer on a support surface. 19. The method of malcing a luminescent screen comprising the steps of:

washing a quantity of base particles with a protective colloid suspension to provide a first adsorbent film on said -base particles, then washing sa-id fbase particles with a liquid dispersion containing colloidal particles of a first phosphor to provide a layer thereof on said rst adsorbent film, then washing said -base particles with said protective colloid suspension to provide a second adsorbent film on the layer of colloidal particles of said first phosphor, then washing said base particles with a liquid dispersion containing colloidal nonluminescent particles -to provide a layer thereof on said second adsorbent film, then Washing said base particles With said protective colloid suspension to prov-ide a third adsorbent film 0n said layer of nonluminescen-t particles, and then washing said base particles with a liquid dispersion containing colloidal particles of a second phosphor to provide Ia layer thereof -on said third adsorbent film,

and then depositing the coated particle product of the above-named steps ina layer on a substrate.

20. The method accordingto claim 19 and wherein said base particles are phosphor particles of a size larger than said colloidal particles and wherein said base phosphor particles luminesce in a color different from lthat of either said first or second colloidal phosphor particles.

21. The method of making a luminescent screen comprising a multiplicity of fractional areas each of which includes a plurality of superimposed layers of different color light emitting phosphors, said method comprising the steps of:

bathing a quantity of base particles of a first phosphor of given sizes in an acidic protective colloid solution to coat said base particles with a first film of said protective colloid, then bat-hing said base particles in water, then bathing said base particles in a liquid dispersion containing nonluminescent particles which are many times smaller than said given sizes, then bathing said base particles in water, then bathing said base particles in an acidic protective colloid solution to coat said base particles with a second fihn of said protective colloid, Ithen bathing said base particles in Water,

then agitatedly bathing said base particles in an acididied liquid dispersion containing paricles of a Second phosphor which .are many times smaller than said given sizes,

then bathing said base particles in Water,

then bathing said base particles in an acidic protective colloid solution to coat said 'base particles with a third ilm of Ysaid protective colloid,

then bathing said base particles in water,

then bathing said base particles in a liquid dispersion containing nonluminescent particles which are many times smaller than said given sizes,

then bathing said base particles in water,

"then bathing said base particles in an acidic protective colloid solution to coat said base particles with a fourth `i'ilm of said protective colloid,

then bathing said base particles in Water,v

then agitatedly bathing said base particles in an aciditied liquid dispersion con-taining particles of a third phosphor iwhich are many times smaller than said given sizes,

then bathing said'base particles in Water,

then depositing said base particles in a layerupon a substrate,

then alumin-izing said layer,

and then subjecting said aluminized layer to a bakeout.

22. The method of making a luminescent screenac-v gelatin and polyvinyl alcohol, and each of `said acidiiied` phosphor dispersions has` a pH of about` 5.

References: Cited by the Examiner UNITED STATES PATENTS l Drapeau et al. 117-100 `Jenkins 117-335` Walison 117-335 Malter `117-`-33.5 Painter 117-335"v Sadowsky 117-335 Fonda 117-335 Welch 117-335 Y Marleoski -..I 117-100 lMears 117-49 X Teves .J'. 117-335 Levin et al 117-335 Rhl'burg et al. 117-335 Togias 117-335 Umberger et al.k 117-100V EilandY 117-49 WILLIAM D. MART1N,'Primary Examiner.V

S. W. ROTHSTEIN, Assistant Examiner. 

1. THE METHOD OF MAKING A STRUCTURE COMPRISING THE ELEMENTS OF: (A) A SUPPORT SURFACE AND (BY COLLOIDAL SOLID PARTICLES, SAID METHODS COMPRISING THE STEPS OF: (1) COATING ONE ONLY OF SAID ELEMENTS WITH A PROTECTIVE COLLOID PARTICLE-ADSORPTIVE MATERIAL, WHEREBY AT LEAST A PORTION OF SAID MATERIAL IS ADSORBED TO SAID ONE OF SAID ELEMENTS, (2) THEN WASHING SAID ONE OF SAID ELEMENTS IN A SOLVENT FOR SAID MATERIAL TO REMOVE UNADSORBED MATERIAL FROM SAID ONE OF SAID ELEMENTS, (3) THEN DISPERSING SAID SOLID PARTICLES IN A QUANTITY OF A LIQUID WHICH IS DEVOID OF SAID MATERIAL AND IN WHICH SAID PARTICLES ARE INSOLUBLE, (4) AND BATHING SAID SUPPORT SURFACE WITH SAID DISPERSION TO ADSORPTIVELY ADHERE SAID PARTICLES TO SAID SUPPORT SURFACE. 